REXECD(8) BSD System Manager's Manual REXECD(8)NAME
rexecd -- remote execution server
SYNOPSIS
rexecd
DESCRIPTION
rexecd is the server for the rexec(3) routine. The server provides remote execution facili-
ties with authentication based on user names and passwords.
rexecd listens for service requests at the port indicated in the ``exec'' service specifica-
tion; see services(5). When a service request is received the following protocol is initi-
ated:
1. The server reads characters from the socket up to a NUL ('\0') byte. The resultant
string is interpreted as an ASCII number, base 10.
2. If the number received in step 1 is non-zero, it is interpreted as the port number of a
secondary stream to be used for the stderr. A second connection is then created to the
specified port on the client's machine.
3. A NUL terminated user name of at most 16 characters is retrieved on the initial socket.
4. A NUL terminated, unencrypted password of at most 16 characters is retrieved on the
initial socket.
5. A NUL terminated command to be passed to a shell is retrieved on the initial socket.
The length of the command is limited by the upper bound on the size of the system's
argument list.
6. rexecd then validates the user as is done at login time and, if the authentication was
successful, changes to the user's home directory, and establishes the user and group
protections of the user. If any of these steps fail the connection is aborted with a
diagnostic message returned.
7. A NUL byte is returned on the initial socket and the command line is passed to the nor-
mal login shell of the user. The shell inherits the network connections established by
rexecd.
DIAGNOSTICS
Except for the last one listed below, all diagnostic messages are returned on the initial
socket, after which any network connections are closed. An error is indicated by a leading
byte with a value of 1 (0 is returned in step 7 above upon successful completion of all the
steps prior to the command execution).
username too long
The name is longer than 16 characters.
password too long
The password is longer than 16 characters.
command too long
The command line passed exceeds the size of the argument list (as configured into
the system).
Login incorrect.
No password file entry for the user name existed.
Password incorrect.
The wrong password was supplied.
No remote directory.
The chdir(2) to the home directory failed.
Try again.
A fork(2) by the server failed.
<shellname>: ...
The user's login shell could not be started. This message is returned on the con-
nection associated with the stderr, and is not preceded by a flag byte.
SEE ALSOrexec(3)HISTORY
The rexecd command appeared in 4.2BSD.
BUGS
Indicating ``Login incorrect'' as opposed to ``Password incorrect'' is a security breach
which allows people to probe a system for users with null passwords.
A facility to allow all data and password exchanges to be encrypted should be present.
SECURITY CONSIDERATIONS
As the passwords exchanged by the client and rexecd are not encrypted, it is strongly recom-
mended that this service is not enabled.
BSD June 1, 1994 BSD